diff --git a/cmd/wasm/main.go b/cmd/wasm/main.go
index 33a7eba..7ce280f 100644
--- a/cmd/wasm/main.go
+++ b/cmd/wasm/main.go
@@ -25,32 +25,19 @@ func renderToString(_ js.Value, args []js.Value) any {
 	if len(args) >= 2 && args[1].Type() == js.TypeString {
 		locale = args[1].String()
 	}
-	ctx := html.NewContext(locale)
-
-	layout := html.NewLayout(variant)
+	slots := make(map[string]html.Node)
 
 	if len(args) >= 3 && args[2].Type() == js.TypeObject {
-		slots := args[2]
+		jsSlots := args[2]
 		for _, slot := range []string{"H", "L", "C", "R", "F"} {
-			content := slots.Get(slot)
+			content := jsSlots.Get(slot)
 			if content.Type() == js.TypeString && content.String() != "" {
-				switch slot {
-				case "H":
-					layout.H(html.Raw(content.String()))
-				case "L":
-					layout.L(html.Raw(content.String()))
-				case "C":
-					layout.C(html.Raw(content.String()))
-				case "R":
-					layout.R(html.Raw(content.String()))
-				case "F":
-					layout.F(html.Raw(content.String()))
-				}
+				slots[slot] = html.Raw(content.String())
 			}
 		}
 	}
 
-	return layout.Render(ctx)
+	return renderLayout(variant, locale, slots)
 }
 
 // registerComponents defines custom elements from the HLCRF slot map.
diff --git a/cmd/wasm/render_shared.go b/cmd/wasm/render_shared.go
new file mode 100644
index 0000000..42187e4
--- /dev/null
+++ b/cmd/wasm/render_shared.go
@@ -0,0 +1,35 @@
+// SPDX-Licence-Identifier: EUPL-1.2
+
+package main
+
+import html "dappco.re/go/core/html"
+
+// renderLayout builds an HLCRF layout from slot nodes and renders it.
+// The helper is shared by the JS entrypoint and host-side tests so the
+// slot-to-layout mapping stays covered outside the wasm build.
+func renderLayout(variant, locale string, slots map[string]html.Node) string {
+	ctx := html.NewContext(locale)
+	layout := html.NewLayout(variant)
+
+	for _, slot := range canonicalSlotOrder {
+		node, ok := slots[slot]
+		if !ok || node == nil {
+			continue
+		}
+
+		switch slot {
+		case "H":
+			layout.H(node)
+		case "L":
+			layout.L(node)
+		case "C":
+			layout.C(node)
+		case "R":
+			layout.R(node)
+		case "F":
+			layout.F(node)
+		}
+	}
+
+	return layout.Render(ctx)
+}
diff --git a/cmd/wasm/render_shared_test.go b/cmd/wasm/render_shared_test.go
new file mode 100644
index 0000000..7288cbf
--- /dev/null
+++ b/cmd/wasm/render_shared_test.go
@@ -0,0 +1,49 @@
+//go:build !js
+
+// SPDX-Licence-Identifier: EUPL-1.2
+
+package main
+
+import (
+	"testing"
+
+	html "dappco.re/go/core/html"
+)
+
+func TestRenderLayout_RendersSlotsInVariantOrder(t *testing.T) {
+	got := renderLayout("HCF", "en-GB", map[string]html.Node{
+		"H": html.Raw("head"),
+		"C": html.Raw("body"),
+		"F": html.Raw("foot"),
+	})
+
+	want := `<header role="banner" data-block="H-0">head</header>` +
+		`<main role="main" data-block="C-0">body</main>` +
+		`<footer role="contentinfo" data-block="F-0">foot</footer>`
+	if got != want {
+		t.Fatalf("renderLayout() = %q, want %q", got, want)
+	}
+}
+
+func TestRenderLayout_UsesLocaleAwareTextNodes(t *testing.T) {
+	got := renderLayout("C", "fr-FR", map[string]html.Node{
+		"C": html.El("p", html.Text("prompt.yes")),
+	})
+
+	want := `<main role="main" data-block="C-0"><p>o</p></main>`
+	if got != want {
+		t.Fatalf("renderLayout() with locale = %q, want %q", got, want)
+	}
+}
+
+func TestRenderLayout_IgnoresMissingAndUnknownSlots(t *testing.T) {
+	got := renderLayout("C", "en-GB", map[string]html.Node{
+		"C": html.Raw("content"),
+		"X": html.Raw("ignored"),
+	})
+
+	want := `<main role="main" data-block="C-0">content</main>`
+	if got != want {
+		t.Fatalf("renderLayout() with unknown slots = %q, want %q", got, want)
+	}
+}